How to Store Torque Tools? Storage Rules and Calibration

A torque tool is a measuring instrument. Its accuracy depends on how it is used, but also on the conditions in which it is stored between jobs. ISO 6789-2, the standard according to which hand torque wrenches and screwdrivers are calibrated, lists storage conditions among the factors that determine the length of the calibration interval. A tool kept in poor conditions simply has to be checked more often.

The most important storage rules:

• store a spring-mechanism wrench with the setting wound back to the lowest value on the scale, never below it and never to zero,
• before putting the tool away, clean off grease and oil, remove the sockets and place it in its case,
• keep the tool in a dry room with a stable temperature, away from radiators and sunlight, and keep electronic tools away from magnets as well,
• remove the batteries from electronic tools before longer periods of non-use,
• after a break of several months, inspect the tool, perform a few test releases and check the calibration due date.

Below we explain where these rules come from and how storage differs between the various types of torque tools.

Why is a spring wrench stored with the setting wound back?

In click, break-back and slip-clutch wrenches, the release torque is determined by a spring that presses on the parts of the mechanism. Turning the handle increases its compression. The higher the setting, the more the spring is compressed.

A spring left under high load for a long time gradually loses its elasticity. The wrench then starts to release at a torque lower than the one set on the scale. The joint is tightened less than the documentation requires, while the wrench still gives a completely normal click. The user therefore has no way of noticing the problem during work.

That is why, after finishing work, you should set the scale to the lowest value in the range of the model. For a 20–100 Nm wrench this will be 20 Nm, and for a 60–300 Nm wrench it will be 60 Nm. With most manufacturers, the lower limit of the scale is around 20% of the wrench's maximum torque.

Can the setting be wound back to zero?

Many users turn the handle all the way to the stop, below the scale, because they believe a fully relaxed spring is the safest option. Manufacturers recommend otherwise. The British torque wrench manufacturer Norbar explicitly advises against going below the lowest mark on the scale and setting the wrench to zero, as this may disturb its calibration. Below the range, the spring loses its preload and the parts of the release mechanism may shift relative to each other.

The lowest scale value combines two advantages: the spring is relieved, and the mechanism keeps a stable position. If the instructions for your wrench specify a different procedure, follow the instructions, because the manufacturer knows the design of its mechanism.

Does the wrench have to be released after every tightening?

Norbar states that an occasional user should wind back the setting after each job. For wrenches used many times a day, e.g. on an assembly line or in a workshop, leaving the setting between tightenings does not damage this manufacturer's wrenches. The same manufacturer points out that the torque applied to a bolt is affected far more by how the wrench is handled than by whether it was released.

In practice, we recommend a simple rule: release a wrench used daily at the end of the shift and before every longer break. Release a wrench used a few times a year, e.g. for a machine inspection or seasonal tyre change, immediately after work, because it will lie like that for weeks or months. Always check the manufacturer's guidelines and follow its instructions.

If the wrench passes through the hands of many people and it is difficult to make sure it is released, consider a model with a torsion bar mechanism, described in the next section. You will find both solutions among mechanical torque wrenches. Setting the torque, working technique and the most common tightening mistakes are described in the article How to tighten bolts with a torque wrench.

How should other torque tools be stored?

The rule of winding back the setting applies to tools in which torque is determined by a loaded spring. Other designs require different care.

• Wrenches with a torsion bar mechanism. In Stahlwille MANOSKOP 730 wrenches, the release mechanism works on a flexible bar instead of a coil spring. The bar remains unloaded until you tighten a bolt, so the manufacturer does not require the setting to be wound back after work. These wrenches still need to be kept clean, stored in a case and calibrated regularly.
• Electronic wrenches and screwdrivers. Torque is measured by a strain gauge sensor, so there is no spring to release. Durability depends on the electronics. Before putting the tool away, switch it off and transfer the stored results to your system. If the tool is to be stored for a longer time, remove the batteries, as electrolyte leakage damages contacts and electronics. Instructions for electronic wrenches also recommend keeping them away from magnetised objects, dust and sand. Manufacturers specify separate operating and storage temperature ranges. The most common operating range is 5–42°C and the storage range is −20 to +50°C. It is worth checking these values for your model. The design differences between the two groups are described in the article Electronic or mechanical torque wrench, and an overview of models can be found in the electronic torque wrenches category.
• Wrenches and screwdrivers without a scale, set with a tester. These tools remain set to the working torque, because every change of setting requires readjustment on a tester. Remember that production wrenches set to a single fixed torque should be checked regularly on a torque tool tester to make sure the measurement results are correct.
• Mechanical screwdrivers with a scale. Adjustable torque screwdrivers have a spring, so apply the same rule as for spring wrenches, unless the instructions say otherwise.
• Torque tool testers. A tester is used to check other tools, so its accuracy affects every wrench checked on it. Store it in a case, in a fixed place, with the same precautions as electronics. Torque tool testers also require periodic calibration.
• Battery torque multipliers. Disconnect the lithium-ion battery from the tool and store it partially charged. Manufacturers most often recommend 30–50%, and the exact value is given in the instructions. Check the charge level every few months.

Storage guidelines for different types of torque tools

Where should torque tools be stored?

Before the tool goes back to its place, clean it with a dry, lint-free cloth. In particular, remove grease and oil residues. They can deform plastic parts, and a slippery handle makes it harder to grip the tool securely during the next job. Do not immerse the wrench in solvent or a parts washer, as the liquid may wash the grease out of the mechanism. If you have a storage case with foam inserts, remove the sockets and bits so that the tool fits exactly in its slot.

The best place is the original case or pouch. The wrench lies in a shaped slot, does not move and is protected against impacts and dust. A tool thrown loosely into a toolbox or drawer knocks against other tools, and impacts on the ratchet, scale or display affect how it works. Keep the case horizontal and do not place heavy objects on it.

The room should meet several conditions:

• Dry storage. Moisture causes corrosion of the drive square, ratchet and mechanism parts, and in electronic tools also of the battery contacts.
• Stable temperature. Keep tools away from radiators, heaters, sunlit windows and welding stations.
• Away from magnets. This applies to electronic tools. Magnetic strips on the wall above the workbench and magnetic holders are a common cause of problems.
• A fixed place. In a company, every tool should have its own place, an inventory number and an assigned next calibration date. A copy of the calibration certificate stored together with the tool is useful during audits.

An unheated garage, a site container or a factory hall in winter are places where moisture condenses on cold metal. If you have no other place, use a sealed case and put a moisture absorber sachet, e.g. silica gel, inside it, replacing it from time to time. When a cold tool is brought into a warm room, water vapour condenses on its surface. Leave it in the open case until it has dried completely, and only then close the case.

How should torque tools be transported?

The same rules apply during transport as in the tool cabinet. Transport a spring wrench with the setting wound back, always in its case. Secure the case against sliding and do not transport it together with heavy tools that could fall on it when braking.

A service vehicle is a poor place to store tools overnight or over the weekend. The interior of a car heated by the sun can exceed 60°C, which is above the storage range specified for many electronic wrenches. In winter, a tool taken out of a cold car quickly becomes covered with moisture in a warm room. If the tools have to stay in the car, choose a place shielded from the sun and remove the batteries from electronic devices.

What should you do with a tool after longer storage?

A tool that has been stored for several weeks or months needs a short preparation before the first tightening:

1. Inspect the tool. Check that the ratchet works smoothly without play, that the scale is legible, that there is no corrosion on the drive square and that the handle is not cracked. On electronic tools, check the display and battery contacts.
2. Perform a few test releases. Set a low or medium value and release the wrench several times, ideally about five. This distributes the grease in the mechanism and returns it to normal operation.
3. Check the tool on a tester. Before tightening critical joints, compare the readings on a torque tool tester. Such a check does not replace calibration, but it quickly shows whether the wrench is within the required tolerance.
4. Check the calibration due date. If the user does not have their own tool control procedure, ISO 6789-2 assumes a default interval of 12 months or 5,000 cycles, whichever comes first. A wrench put away after use has already started this period. If the tool is stored in difficult conditions, it is worth shortening the interval, as the standard explicitly lists storage conditions among the criteria for choosing it.
5. Have it calibrated after a drop. According to ISO 6789-2, a tool must be calibrated after an overload, after a repair and after any improper handling that may have affected its performance. A case falling from a shelf or a wrench dropped from a height is exactly such a situation, even if no damage is visible from the outside.

If the due date has passed or the tool raises doubts, have it calibrated before continuing work. After calibration you will receive a certificate confirming the condition of the tool.

If you use a torque tool only a few times a year, which applies especially to high-torque tools such as torque multipliers or hydraulic wrenches, consider renting the tool for the specific job. This avoids the costs of storage and periodic calibration.